Witnesses say the AU troops were fired on as their convoy moved through the capital late Wednesday. The soldiers returned fire, and the resulting gun battle killed at least one civilian. At least four others were wounded.

Two police officers were shot and killed in Mogadishu earlier in the day. The officers were gunned down as they checked vehicles for weapons on a road leading to the airport.

Several hundred African Union peacekeepers from Uganda have arrived in Mogadishu this week. The peacekeepers are there to help Somalia's transitional government stabilize the war-torn country.

The government has struggled to contain violence in the capital since its forces, along with Ethiopian troops, drove out a rival Islamist movement in December.

The AU hopes to gather 8,000 troops in all, but member nations have so far pledged only half that number. The force will replace the Ethiopians, who Addis Ababa intends to gradually withdraw.

The insurgents in Somalia are believed to be a mix of defeated Islamists and clan leaders resisting the transitional government.